Method for increasing the safety against firedamp ignitions during blasting in underground mining and blasting elements used for said purpose

ABSTRACT

The present disclosure is directed to a method for preventing firedamp ignitions during blasting in underground mining which comprises separating the space where the explosive charge is to be detonated from the space where the firedamp is present by providing therebetween a zone containing a layer in the form of, for example, a paste or a foam containing a liquid in a uniform distribution. The present disclosure is also directed to blasting elements for preventing said firedamp ignitions.

United States Patent Berthmann et al.

Inventors: Adolf Berthmann; Paul Lingens, both of Leverkusen; Ernst Morhenn, Beuel, all 0 Germany Assignee: Dynamit Nobel Aktiengesellschaft, TroisdQFLGPUP LYW V a, Filed: Mar. 18, 1969 Appl. No.: 808,293

US. Cl ..l02/23 Int. Cl ..F42d 5/00 Field of Search ..102/22-24; 169/ 1 169/2 SHOT HOLE Wl/l/l w i LASTINC CARTRIDGES -2 Mar. 14, 1972 Primary Examiner-Verlin R. Pendegrass Attorney-Craig, Antonelli, Stewart & Hill [57] ABSTRACT The present disclosure is directed to a method for preventing firedamp ignitions during blasting in underground mining which comprises separating the space where the explosive charge is to be detonated from the space where the firedamp is present by providing therebetween a zone containing a layer in the form of, for example, a paste or a foam containing a liquid in a uniform distribution. The present disclosure is also directed to blasting elements for preventing said firedamp ignitions.

7 Claims, 2 Drawing Figures PASTE LAYERJ HEIGHT 0F FACE s .E AMSLAYERV f 4 .,r

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ROCK 0R COAL Patented March 14,1972 3,648,614

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INVEN ADOLF BERTHM PAUL LINGENS ERNST MORHENN BY Rm r x' l,

ATTORNEYS METHOD FOR INCREASING THE SAFETY AGAINST FIREDAMP IGNITIONS DURING BLASTING IN UNDERGROUND MINING AND BLASTING ELEMENTS USED FOR SAID PURPOSE BACKGROUND OF THE INVENTION The present invention relates to a procedure for increasing the safety against firedamp ignitions during blasting in underground mining.

In connection with blasting in underground mining, a compulsory prerequisite is the tamping of the charges, that is, the damming up of the explosive charges in order to provide protection against firedamp explosion with a possible subsequent coal dust explosion. Water has proven to be a particularly suitable tamping material since it does not only produce an effective tamping of the charge but also it considerably reduces the detrimental dust-enriched afterdamp. The water is utilized in a conventional manner in the form of water tamp cartridges or in the form of aqueous pastes, wherein the shot holes are sealed after the explosive charge has been inserted.

As in the likewise-conventional face saturation (soaking) blasting method, the water is disposed within the shot hole. This, of course, imposes certain restrictions with respect to the amount of tamping that can be used and the distribution thereof. As a consequence, the amount of tamping available is not sufficiently large in many instances for distributing the moisture uniformly and, in particular, over the entire blasting range, so that in spite of the tamping, firedamp explosions are possible under certain conditions. An additional safety-undermining factor occurs when fissures are present in the rock or in the coal seam, despite the tamping provided in the shot hole, so that there can occur hot gas clouds or the like at the breast of the face outside the shot hole which may lead to the ignition of any firedamp mixture present at that site.

Another conventional method which is frequently utilized is one wherein, in the front of the breast of the face or at the mine working area, a bag filled with water is provided and is caused to rupture or burst by means of a separate, small amount of explosive charge disposed in the bag. This is effected shortly before the ignition of the explosive introduced into the shot holes. This method is suppose to distribute or spray the water substantially uniformly over the entire cross section of the area and thus prevent the ignition of any firedamp mixture that may be present. However, this method is likewise beset by many deficiencies. Thus, it can happen, for example, that due to inadvertence, the explosive disposed in the shot hole is ignited earlier than the explosive provided for rupturing the bag and spraying the water, so that the bag explosive charge is not at all detonated, due to failure of the detonator (primer), perhaps due to a short circuit. Thus, the water present in the bag is sprayed too late, in the former case, and is not sprayed at all, in the latter case. Furthermore, it is readily possible in this method that only a small portion of the water provided in the bag is distributed by spraying in the desired manner, and that the larger portion splashes without any efiect, onto the bottom of the mine tunnel. This, of course, renders the effective prevention of a firedamp explosion very doubtful, at the very least.

SUMMARY OF THE INVENTION An objectof the present invention is to avoid the prior art disadvantages in preventing firedamp ignitions during blasting in underground mining.

Another object of the present invention is to provide an improved method for increasing the safety against firedamp ignitions during blasting in underground mining.

Another object of the present invention is to provide an improved method 'of preventing firedamp ignitions during blasting in underground mining wherein it is possible to apply water or aqueous solutions in sufficient quantities, readily, rapidly and uniformly to the blasting site or the breast of the mine face.

Still another object of the present invention is to provide an improved method for preventing firedamp ignitions during blasting in underground mining wherein the dust produced during said blasting, which is detrimental to health, can be substantially reduced.

A still further object of the present invention is an improved blasting element which produces the advantageous features previously mentioned.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description, and the drawings to which this description refer, wherein:

FIG. 1 is a schematic diagram of the working face of the mine with the loaded shot holes arranged therein; and

FIG. 2 is an enlarged view of a single-shot hole.

Pursuant to the present invention, it has been found that the above-mentioned disadvantages may be eliminated and a much improved method for increasing the safety against firedamp ignitions during blasting in underground mining may be obtained wherein, as seen in FIGS. 1 and 2, after the shot holes 1 have been produced and charged with an explosive 2, a layer of a paste 3 which is rich in water or another aqueous solution is applied at the breast area of the face, extending over the entire cross-sectional area thereof. The paste adheres to the rock and/or to the coal, and does not flow off therefrom. The blasting cartridges may be ignited electrically in a conventional manner by a primer 5, as seen in FIG. 2. In like manner, a layer or stopper (plug) made of a correspondingly composed foam 4 can also be utilized. In this manner, the space where the explosive charge is to be detonated is safely and reliably separated from the space where the firedamp is present, that is by means of a layer spanning the cross section of the face, said layer containing water in a uniform distribution. While FIG. 1 shows the use of both the paste layer 3 and the foam stopper 4, it should be understood that in practice only one or the other medium would be used.

The paste or the foam should contain as much water or aqueous solution as possible, but on the other hand, it should be sufficiently rigid and stable so as to have a self-supporting consistency such that even when a long period of time elapses before blasting, there does not take place any sliding, running or sagging of the paste or foam. Thus, the water contained in the paste or in the foam is securely held in front of the face. For this purpose, it is possible, in accordance with a further embodiment of the present invention, to additionally introduce into the paste, air or an inert gas, which can, if desired, be accomplished during the application of the layer onto the breast of the face. Also, the foam can be produced with an inert gas, instead of with air. The effect of this measure can be further enhanced by adding surface-active substances, for example surfactants, in a conventional manner.

In a further feature of the present invention, it is frequently advantageous to add substances to the water or the aqueous solution which have a flame-extinguishing effect and/or exert a favorable effect on the deleterious components of the afterdamp, for example by absorbing the nitrous gases (nitrogen peroxide) produced during each detonation. Suitable substances include, for example, the chlorides, the carbonates and the phosphates of alkali and alkaline earth metals.

It is to be understood that the paste or the foam is applied to the breast of the face in a layer, the thickness of which depends upon the particular conditions. In any event, a sufficient thickness is uniformly distributed over the cross section of the face. Of course, when a foam is employed, the required thickness of the layer will have to be larger than when a paste is utilized. In any event, the safety factor for preventing the igmtion of any explosive firedamp mixture present in the entire mine working area and in front of the face will be larger. the thicker the layer. When foam is employed. this layer can also assume the shape of a foam plug disposed at the breast of the face or at a greater or lesser distance therefrom.

The foam can be also produced directly in front of the face hy means of a compressor. When a foam is used, it is desirable to employ methane-free air from the compressed air network which is provided in the proximity of the mine face, or inert gases, such as for example, nitrogen or carbon dioxide. rather than the ambient air located at the mine fore-field (dead face). This ensures that there is a completely methane-free .zone between the explosive and the detonators, on the one hand, and any ignitable firedamp mixture which may be present at a mine face, on the other hand, which zone affords the largest degree of safety possible against a firedamp explo- The process of the present invention is not only distinguished by the fact that it offers a maximum amount of safety against firedamp explosions, but also by the fact that it is possible by means of this process to apply water or aqueous solutions in sufficient quantities, readily, rapidly and uniformly to the blasting site or the breast of the mine face. In this connection, the uniform distribution of the water or aqueous solutions can be easily and efficiently checked before the blasting is conducted. Another advantage necessarily connected with the above features is the fact that the dust produced during blasting, which is detrimental to health, is likewise substantially reduced.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will become more fully understood by referring to the following examples which are given for purposes of illustration only and thus should not be considered as limitative of the present invention.

EXAMPLE 1 A paste having sufficient rigidity and adhesiveness was produced in the following manner. Guar flour (Guar gum) is mixed by agitation with methanol at a ratio of l to 0.8 in a dry bucket. Then, in one pouring step and under vigorous agitation, water is added in an amount such that a percent mixture of guar flour in water is produced. The swelling, which lmmediately commences, is completely terminated after about .3 to 3 hours. A lump-free paste is produced in this manner. that flour (Guar gum) is a swelling agent produced by the ground-up seeds of the guar plant. It is widely utilized, espeeially in the United States, for foodstuffs, for paper manufacture. and also for aqueous explosives.

By means of this aqueous paste which can be applied to a wall by hand, pneumatically hurled against the wall, or also sprayed onto the wall, it is possible to produce on vertical walls a layer with a thickness of several centimeters. Even after 3 days and at a temperature of +40 C no running of the paste could be detected.

By using this paste, the safety against firedamp explosion exhibited by a Class I explosive can be tested. This is done in a test zone. A Class I explosive (Wetter-Nobelit B) is the German safety classification for safety mining explosives. Class I is that class having the least safety against firedarnp. The explosive "Wetter-Nobelit B" consists mainly of blasting gelatin, l.e., nitroglycerin, nitrocellulose, etc., about 30 percent by weight ammonium nitrate, and common salt.

lln accordance with the official test of the mining regulations regarding the sale of explosive to mining works, the explosive lS detonated in a mortar having a bore of 55 mm. inside diameter and a length of 600 mm. without any tamping from the mouth of the bore. No ignition of the firedamp mixture ocpurred in the test zone. in contrast thereto, when the detonation is conducted in the extreme depth of the bore of the mortar, there results in all cases, as is also generally known, an ighition of the firedamp mixture containing 9 percent of methane in the text zone, even when employing only three cartridges of a gelatinized explosive of Class I, known under the commercial name of Wetter-Nobelit B. However, when providing a layer of paste having a thickness of about 2 cm. on a sheet of thin paper glued in front of the shot hole mouth in order to prevent the penetration of paste into the shot hole, no ignition of the firedamp was observed. Even when using five cartridges of the above-mentioned explosive in the mortar, no firedamp ignition takes place.

EXAMPLE 2 From a foaming agent obtained commercially under the name of Tuba (foam-producing substances containing protein bodies) and consisting of a mixture of various soaps, a foam is produced having a density of 0.032 g./cm. corresponding to a water content of about 3.2 volume percent. During tests this foam readily exhibited a durability of about 30 minutes at temperatures of up to +50 C.

in a round (circular) mortar having a bore hole diameter of 40 mm. and a length of 2,000 mm., a cartridge of a rock blastmg agent with the commercial name of Ammon-Gelit 2 (a brisant rock blasting explosive customarily used in Germany with blasting gelatin, i.e., nitroglycol, trinitrotoluene, dinitrotoluene, nitrocellulose, about 38 percent by weight ammonium nitrate, and wood dust) having a diameter of 25 mm. [5 axially disposed and centered with a spacing of 10 mm. from the mouth of the bore hole. When blasting into a firedamp mixture of the test zone containing 9 percent methane, there always takes place a grave firedamp explosion. When providmg in front of the bore hole a layer of the above-mentioned foam with a thickness of about 5 cm., a firedamp explosion also takes place, but it is considerably weaker. When providing a foam with a thickness of about 10 cm. in front of the bore hole, no firedamp ignition occurred. The penetration of the foam into the bore hole was always prevented by means of a thin sheet of paper.

in the test zone, a firedamp safety explosive of Class ll hav ing the commercial designation of Wetter-Energit A (relates to a Class ll explosive which is safer with respect to a firedamp mixture than a Class l explosive. The explosive Wetter-Energit A" consists mainly of nitroglycerin, about 10 percent by weight sodium nitrate, and ammonium chloride) is tested in an open rim mortar with respect to its safety against firedamp, in accordance with the official guidelines of the mining regulations regarding the sale of explosives to mining works. Eight cartridges of explosive regularly ignited the firedamp mixture; six cartridges could no longer do so. When the explosive is covered, in the rim (edge) of the mortar, with a foam layer of l5 mm., eight cartridges still effected an ignition. However, when the entire rim is filled with foam, that is when a foam layer having a thickness of 60 mm. is disposed over the explosive, then eight cartridges could not effect any firedamp explosion.

A cartridge having a diameter of 25 mm. and a weight of l00 g. of the rock blasting substance known commercially as Ammon-Gelit 3 (a rock blasting explosive customarily used in Germany, which also has a very strong tendency toward firedamp ignition and consists of blasting gelatin, i.e., nitroglycol, trinitrotoluene, dinitrotoluene, nitrocellulose, about 30 percent by weight ammonium nitrate, and wood dust) is disposed in a polyolefin hose, for example polyethylene, so that it is centered therein. The annular space between the cartridge and the hose is filled with foam. At both ends of the cartridge, in front of the cartridge heads, a foam layer of at least 10 cm. in thickness is provided in the ends of the polyethylene hose, so that the detonating effect of the cartridge in the direction of the longitudinal axis thereof can be neglected. In the case of a hose having an inner diameter of 55 mm. and consequently a thickness of the annular space of 15 mm., the above-mentioned cartridge produced an ignition of the firedamp mixture. However, in the case of an inner diameter of the hose of 60 mm. and accordingly a thickness of the annular space of 17.5 mm. there occurred no ignition.

In a blind test, the annular space between the hose and the cartridge is filled with air. In this instance, 40 g. of the abovementioned rock blasting charge ignited the firedamp mixture, but 30 g. did not ignite said mixture.

For comparison purposes, the annular space between the cartridge and the hose as well as the spaces at the hose ends are filled with water. In this test, in the case of an inner hose diameter of 30 mm. and consequently an annular space with av width of 2.5 mm., the firedamp is ignited, whereas in the case of an inner hose diameter of 32 mm., and a thickness of the annular space of 3.5 mm., no ignition of the firedamp took place.

From this series of tests, the following conclusions can thus be drawn: 40 g. of rock blasting explosive of the above-mentioned type, disposed and centered axially in a polyethylene hose, ignites a firedamp mixture. If water is present in the annular space between the hose and the cartridge, then no ignition takes place starting with an inner hose diameter of 32 mm. and a width of the annular space of 3.5 mm. 1f foam of the above-mentioned type is placed in the annular space between the hose and the cartridge, then no ignition takes place starting with an inner hose diameter of 60 mm. and, correspondingly, a width of the annular space of 17.5 mm. This corresponds to an envelope of foam in the annular space of 333 cm. volume and accordingly an amount of water of 10.7 g. When foam is employed, 10.7 g. of water in finely divided form is thus sufficient to prevent ignition. However, if only water is used in the annular space, then, with an inner hose diameter of 32 mm., 39.3 g. of water, that is almost four times as much, has to be present in the annular space in order to prevent firedamp ignition (explosion).

Any stable and rigid foam which can maintain its form over a long period of time can be employed in the present invention. Suitable foams include, for example, polyurethanes,

polyvinyl materials, e.g., polyvinyl chloride, etc., polystyrene,

the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be apparent to one skilled in the art are intended to be included.

lt is claimed:

1. A method for preventing firedamp ignitions during blasting operations in underground mining after the shot holes have been produced which comprises disposing an explosive in the shot holes so as to be spaced from the working face of the mine, providing a layer rich in an aqueous solution extending across the entire cross section of the working face of the mine at the blast site so as to cover said blast holes, said layer being composed of a substantially self-sustaining medium which adheres to the face of the mine, said layer separating the space where the explosive charge is to be detonated from the space where the firedamp is present and being spaced from the explosive charge.

2. The method of claim 1, wherein said medium is a foam and the foam is produced with an inert gas or air.

3. The method of claim 2, wherein surface-active agents are added to the foam.

4. The method of claim 1, wherein the aqueous solution contains at least one substance selected from the group consisting of the chlorides, the carbonates and the phosphates of alkali and alkaline earth metals, said substance producing a flame-extinguishing and a gas absorbing effect.

5. The method of claim 1, wherein said medium is a paste and the paste is prepared by mixing guar flour with methanol at a ratio of about 1 to 0.8, then adding water to the mixture in an amount such that a 10 percent mixture of guar flour in water is produced and finally permitting the mixture to swell to a lump-free paste.

6. The method of claim 1, wherein said medium is a foam and the foam has a density of about 0.032 g./cm. and a water content of about 3.2 volume percent.

7. The method of claim 1, wherein said medium is a layer of 

1. A method for preventing firedamp ignitions during blasting operations in underground mining after the shot holes have been produced which comprises disposing an explosive in the shot holes so as to be spaced from the working face of the mine, providing a layer rich in an aqueous solution extending across the entire cross section of the working face of the mine at the blast site so as to cover said blast holes, said layer being composed of a substantially self-sustaining medium which adheres to the face of the mine, said layer separating the space where the explosive charge is to be detonated from the space where the firedamp is present and being spaced from the explosive charge.
 2. The method of claim 1, wherein said medium is a foam and the foam is produced with an inert gas or air.
 3. The method of claim 2, wherein surface-active agents are added to the foam.
 4. The method of claim 1, wherein the aqueous solution contains at least one substance selected from the group consisting of the chlorides, the carbonates and the phosphates of alkali and alkaline earth metals, said substance producing a flame-extinguishing and a gas absorbing effect.
 5. The method of claim 1, wherein said medium is a paste and the paste is prepared by mixing guar flour with methanol at a ratio of about 1 to 0.8, then adding water to the mixture in an amount such that a 10 percent mixture of guar flour in water is produced and finally permitting the mixture to swell to a lump-free paste.
 6. The method of claim 1, wherein said medium is a foam and the foam has a density of about 0.032 g./cm.3 and a water content of about 3.2 volume percent.
 7. The method of claim 1, wherein said medium is a layer of paste having a thickness of at least about 3 cm., and disposed on a sheet of thin paper glued in front of the shot hole mouth in order to prevent the penetration of paste into the shot hole. 